Cardiac dysrhythmias such as atrial fibrillation and flutter affect about 2.4 million Americans, with approximately 160,000 new cases in the US alone every year. Electrophysiological (EP) and radiofrequency (RF) ablation procedures to treat cardiac arrhythmias are among the most prolonged and detailed due to the difficulties in the guidance of catheter based diagnostic and therapeutic devices within the cardiovascular system. Although fluoroscopy is still the gold standard imaging tool, it is well recognized that with longer and more challenging procedures, new and more effective real time spatial mapping tools are vitally needed to improve clinical outcomes and to reduce the fluoroscopic radiation doses to which patients are currently exposed. Also a recent review of ablation methods in Circulation stated that "Radiofrequency is the dominant energy source used but remains inadequate to ensure lesion continuity and permanence without an unacceptable increase in procedural time and complications. New, effective, and safe alternative energy sources are needed to achieve the ultimate goal of a single, widely applicable, curative procedure for all forms of AF (atrial fibrillation)." Our project is targeted at this major cardiovascular problem in our aging population concordant with the mission of the National Heart, Lung, and Blood Institute. Our Partnership of clinicians, electrophysiologists and engineers from academic institutions and companies is proposing to develop new highly miniaturized and unique intracardiac imaging devices on steerable electrophysiology catheters which can provide 2D and 3D ultrasound imaging to fully integrate imaging, lesion characterization and therapy within the same catheter devices. We also propose: to expand the capabilities for ablation with these devices from RF energy to newer methods including High Intensity Focused Ultrasound (HIFU) and laser ablation both of which can create more focused and discrete continuous lesions. We will also develop and provide on-line capabilities to allow rapid evaluation of the results and effectiveness of EP ablation procedures. These include methods such as thermal strain imaging to assess tissue heating and laser acoustic tissue characterization and ultrasound methods for defining altered mechanical properties of ablated tissue displayed on 3D fusion displays of electroanatomical mapping of the chambers of the heart and the propagation of normal and abnormal conduction of cardiac rhythms. Our proposed project builds on our first 5 years of funding combining the newest most advanced and miniaturized ultrasound transducer technologies and cabling and connection methods, with the ability to integrate imaging and assessment with direct energy delivery for ablation within the same EP catheter-based ablation devices. It is our expectation that the results of our work can improve the efficacy and availability of these complex treatment strategies while reducing procedure duration, radiation exposure and cost. [unreadable] PUBLIC HEALTH RELEVANCE: Serious abnormalities of cardiac rhythms, such as the rapid and irregular rhythms referred to as atrial fibrillation, often require treatment by trans-catheter ablation procedures. These long and complicated procedures have variable success rates and the abnormal rhythm episodes often recur. Our Partnership of clinicians and engineers is planning to develop new catheter-based methods for performing ablation with integration of energy delivery and ultrasound imaging from inside the heart chambers, with the goal of reducing the duration of these procedures, minimizing radiation exposure to the patient and the physician and improving the results of ablation. [unreadable] [unreadable] [unreadable]